1. Technical Field
The present invention relates to a piercing device of a hydroforming mold, and more particularly, to a piercing device of a hydroforming mold, which enables a pierce punch of the pierce device to be replaced in a simpler way.
2. Background Art
FIG. 1 is a perspective view showing a hydroforming mold in which a prior art piercing device is placed on a lower steel. FIG. 2 is a block diagram of the piercing device of a hydroforming mold of FIG. 1.
As shown in FIGS. 1 and 2, a piercing device is placed on a lower steel 1 in a hydroforming mold, and the piercing device includes a pierce cylinder 3 for receiving a hydraulic pressure from hydraulic piping 2, a pierce punch 5 whose front edge portion is inserted into a cavity provided within the lower steel 1 in order to punch a hole through a molding material by a rod 4 operating by the hydraulic pressure of the pierce cylinder 3, a pierce connector 6 for applying the operation of the rod 4 to the pierce punch 5, and a punch holder 7 for holding the pierce punch 5 to the pierce connector 6.
Herein, a recess portion 4′ of a predetermined shape is provided on the rod 4 so as to couple one end portion 6′ of the pierce connector 6 thereto by fitting. More specifically, the one end portion 6′ of the pierce connector 6 is formed longitudinally so as to have a T-shaped cross section, and the recess portion 4′ of the rod 4 is formed corresponding to the shape of the one end portion 6′ of the pierce connector 6 so as to be coupled thereto downward by fitting.
A plurality of fastening holes 3a are formed on the top surface of the pierce cylinder 3, and bolts (not shown) are inserted through the fastening holes 3a to fix the pierce cylinder 3 to the lower steel 1.
The pierce connector 6 and the punch holder 7 are fastened by bolts (not shown), and an adjust plate 8 serving as a washer is placed between the pierce connector 6 and the punch holder 7.
In the thus-constructed piercing device of a hydroforming mold, when the rod 4 is operated by the hydraulic pressure applied from the pierce cylinder 3, the pierce punch 5 connected to the rod 4 by the pierce connector 6 operates to punch a hole through a product.
The pierce punch 5 is abraded after a long period of use. The pierce punch 5 abraded to a large extent increases the fraction defective of holes when punching a hole through a molding material, and thus is required to be replaced by a new pierce punch 5 for use.
The prior art piercing device, however, has drawbacks in that for the replacement of pierce punch 5, the pierce cylinder 3 must first be removed from the lower steel 1.
More particularly, in order to remove the pierce punch from the lower steel 1, firstly, the nuts 2a fastening the hydraulic piping 2 and the pierce cylinder 33 must be released, and then the bolts (not shown) fastened to the fastening holes 3a formed on the top surface of the pierce cylinder 3 must be released.
It is necessary to firstly remove the pierce cylinder 3 because the one end portion 6′ is firmly coupled to the recess portion 4′ of the rod 4 by fitting by downwardly moving the pierce cylinder 3 while tightly adhering the pierce connector 6 to the lower steel 1 upon coupling in order to avoid the pierce connector 6 connected to the rod 4 from unstably moving upon punching the product by using the pierce punch 5.
After removing the pierce cylinder 3 from the lower steel 1, the pierce connector 6, the adjust plate 8, the punch holder 7, and the pierce punch 5 fastened to one another by the bolts (not shown) are sequentially removed from the lower steel 1, and the bolts fastened to the fastening holes 7a formed on the punch holder 7 are released to replace the pierce punch 5.
Meanwhile, it can be assumed that the pierce punch 5 is removed by disassembling only the punch holder 7 without disassembling the pierce cylinder 3 from the lower steel 1. In this case, however, the pierce punch 5 interferes with the pierce cylinder 3 during the removal of the pierce punch 5 inserted into the cavity of the lower steel 1.
As above, in order to remove the pierce punch 5 from the lower steel 1, the man-hour for removing the pierce cylinder 3 in advance is required and it thus takes much time replace the pierce punch 5.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.